With the recent trend for energy saving, there is an increasing demand for lightings and backlights that use LEDs. The LEDs used for these applications are white emitting LEDs of a construction in which a phosphor is disposed on an LED chip that emits light of blue or near ultraviolet wavelengths. Many of such white emitting LEDs use a YAG (yttrium-aluminum-garnet) phosphor that emits a yellow color by using the blue excitation light from a blue LED chip disposed underneath the YAG phosphor.
However, there are problems associated with the YAG phosphor. One problem is that temperature quenching, a phenomenon in which luminance decreases with increase in phosphor temperature, becomes high under high output conditions. Another problem is that luminance seriously degrades when the YAG phosphor is excited by near ultraviolet light (typically, the term “near ultraviolet light” used in conjunction with blue excitation is intended to be inclusive of a range covering purple of about 350 to 420 nm wavelengths) to improve color reproduction range and color rendering properties.
These problems have been addressed by studies of yellow emitting nitride phosphors. Most promising among such nitride phosphors are, for example, the La3Si6N11 phosphors (hereinafter, these types of phosphors will be collectively referred to as “LSN phosphors”, including those in which lanthanum is replaced with other metals) described in Patent Literatures 1 and 2. These publications describe producing LSN phosphors with a variety of fluxes (see paragraph [0248] of Patent Literature 1, and paragraphs [0131] to [0136] of Patent Literature 2).